Control system for magnetic suspension of centrifuge rotors

Claim 1

A CONTROL SYSTEM FOR MAGNETICALLY SUSPENDING A CENTRIFUGE ROTOR AND FOR AUTOMATICALLY MAINTAINING THE ROTOR IN A SELECTED SUSPENDED POSITION COMPRISING A FIRST SERVO MAGNETIC SUSPENSION COIL DISPOSED ABOVE SAID ROTOR AND IN ALIGNMENT WITH THE VERTICAL AXIS OF SAID ROTOR; A DISTANCE DETECTOR COIL AND A SECOND SERVO COIL DISPOSED BENEATH SAID ROTOR AND ALIGNED WITH SAID ROTOR AXIS, SAID FIRST AND SECOND SERVO COILS BEING COUPLED BY A MAGNETIC YOKE TO PROVIDE A CLOSED MAGNETIC LOOP, SAID DETECTOR COIL PROVIDING AN OUTPUT SIGNAL PROPORTIONAL TO THE POSITION OF AND TO ANY AXIAL MOVEMENT OF SAID ROTOR; AN AMPLIFIER NETWORK HAVING FIRST, SECOND, THIRD, FOURTH, FIFTH, AND SIXTH STAGES; A HIGH-PASS FILTER CIRCUIT CONNECTED BETWEEN THE OUTPUT OF SAID DETECTOR COIL AND THE FIRST STAGE OF SAID AMPLIFIER NETWORK; AN ADJUSTABLE SOURCE OF REFERENCE VOLTAGE; A FIRST DIFFERENTIATING NETWORK CONNECTED TO THE OUTPUT OF THE SECOND AMPLIFIER STAGE; MEANS FOR CONNECTING SAID REFERENCE VOLTAGE AND THE OUTPUT OF SAID DIFFERENTIATING NETWORK TO SAID THIRD AMPLIFIER STAGE TO PROVIDE A COMPARISON THEREBETWEEN, SAID THIRD AMPLIFIER STAGE PROVIDING AN OUTPUT ERROR SIGNAL PROPORTIONAL TO ANY DEVIATION FROM A SELECTED ROTOR POSITION; A SECOND DIFFERENTIATING NETWORK CONNECTED TO THE OUTPUT OF SAID THIRD AMPLIFIER STAGE; A BALANCE POTENTIOMETER; MEANS FOR CONNECTING SAID POTENTIOMETER AND THE OUTPUT OF SAID SECOND DIFFERENTIATING NETWORK TO SAID FOURTH AMPLIFIER STAGE TO PROVIDE A COMPARISON THEREBETWEEN, SAID FOURTH AMPLIFIER STAGE PROVIDING AN OUTPUT SIGNAL PROPORTIONAL TO THE ERROR IN THE ROTOR POSITION AND TO THE FIRST AND SECOND TIME DERIVATIVES OF THIS ERROR; A TRANSISTOR GATE NETWORK; A SOLID-STATE, HIGH CURRENT POWER SUPPLY CONNECTED TO THE OUTPUT OF SAID GATE NETWORK; A REFERENCE POTENTIOMETER CONNECTED TO SAID GATE NETWORK FOR PROVIDING A STEADY STATE REFERENCE CURRENT AT THE OUTPUT OF SAID POWER SUPPLY; MEANS FOR CONNECTING THE OUTPUT OF SAID POWER SUPPLY TO SAID FIRST ROTOR SERVO COIL; MEANS CONNECTED TO THE OUTPUT OF SAID POWER SUPPLY FOR REVERSING THE POLARITY THEREOF, FOR FILTERING OUT ANY DERIVATIVE CONTROL SIGNALS THEREFROM, AND FOR FEEDING THE RESULTING SIGNAL TO SAID SECOND SERVO COIL; AND MEANS FOR CONNECTING THE OUTPUT OF SAID SIXTH AMPLIFIER STAGE TO THE INPUT OF SAID GATE NETWORK, WHEREBY ANY ROTOR POSITION ERROR SIGNAL APPEARING AT THE OUTPUT OF SAID SIXTH AMPLIFIER STAGE MODIFIES THE GATE NETWORK OUTPUT SIGNAL THEREBY AUTOMATICALLY VARYING THE CURRENT INPUT TO SAID FIRST ROTOR SERVO COIL TO MAINTAIN SAID ROTOR IN A PREDETERMINED SELECTED POSITION, THE NET TOTAL CURRENT TO BOTH SAID SERVO COILS BEING MAINTAINED AT A CONSTANT VALUE TO THEREBY PROVIDE A SUBSTANTIALLY CONSTANT MAGNETIC FLUX IN SAID CLOSED LOOP.